Quantum communication [1], which offers unbreakable security, is gaining interests on critical applications in di- verse areas including finance, transportation, ...
Integrated Silicon Nanophotonic Antenna Array for Free Space Mobile Quantum Communication SungWon Chung and Fatemeh Rezaiefar Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089, USA
Abstract: For the silicon-photonics implementation of free space mobile quantum communication on a chip, which is based on continuous-variable quantum key distribution (CV-QKD) using Gaussian modulated coherent states (GMCS), we discuss a 64-element integrated nanophotonic antenna array design in a commercial silicon technology for steering photons in free space. Quantum communication [1], which offers unbreakable security, is gaining interests on critical applications in diverse areas including finance, transportation, military, operation, manufacturing, and healthcare. GMCS CV-QKD [2] is a unique chip-scale implementation of quantum communication, which can operate in room temperature and achieve a high secure key rate [3]. To steer photons in free space for GMCS CV-QKD, this work presents a 64-element integrated nanophotonic antenna array design based on a miniature grating coupler fabricated in a 180-nm silicon technology. Compared to conventional antenna array with mechanical servo systems, this chip-scale design provides advantages in size, speed, and power consumption for mobile quantum communication. We designed and fabricated a focusing grating coupler with 1-µm width and less than 4-µm length as a nanophotonic antenna array element with approximately 50% measured radiation efficiency. After reducing the width of the focusing grating couplers from 1 µm to 0.5 µm, multiples of the modified focusing grating couplers can be grouped to construct a one-dimensional antenna array with pitch size less than 2 µm. Simulation results with proper phase predistortion show that this one-dimensional antenna array has a radiation efficiency below 10%, acceptable for GMCS CV-QKD, which requires relatively weak radiation to maintain quantum security. For an 8x8 two-dimensional array consisting of such one-dimensional arrays, the simulated probability of a photon in the reference steering location (Figure 1) shows that the antenna pitch can be larger than the half of photon wavelength λ to maintain quantum security. Instead, when the photon steering range is limited, the antenna pitch below 0.87λ is shown sufficient to keep quantum security by suppressing the side-lobe probability by more than 4.4 times.
Fig. 1: Probability on the location of a single photon emitted by a two-dimensional silicon nanophotonic antenna array with 64 elements and the antenna pitch of λ (first plot) and 0.87λ (second plot) for a photon wavelength λ . The z-axis is the probability density function before normalization (from the far field intensity). The planar x-axis and y-axis correspond to the radian of θ and φ in spherical coordinate system.
References 1. L.-M. Duan et al., Nature 414, 418-418 (2001). 2. F. Grosshans et al., Nature 421, 238-241 (2003). 3. C. Ma et al., Optica 3, 1274-1278 (2016).
Revised 31 Jan 2017 2017 BOSTON PHOTONICS CENTENNIAL CONFERENCE
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